Heretofore, heat-sensitive recording materials have been well known, in which colorless or pale-colored basic dyes and organic or inorganic color developers are brought into contact with each other by the application of heat to produce recorded images by utilizing the color reaction therebetween as disclosed in, for example, U.S. Pat. No. 3,539,375.
Recent remarkable advances in heat-sensitive recording systems have permitted high-speed operation of various kinds of apparatus utilizing a thermal head, such as heat-sensitive facsimiles and heat-sensitive printers. For example, modern heat-sensitive facsimiles can transmit a printed page of A4 size paper (210.times.297 mm) in 20 seconds, and modern heat-sensitive printers can print 120 or more letters per second. With the development of such high-speed facsimiles and printers, it is now required for heat-sensitive recording materials which are used in the high-speed facsimiles and printers to have a high recording sensitivity (dynamic recording characteristics). Furthermore, the materials must cause neither static recording within a low temperature range (60.degree. C. to 70.degree. C.) nor piling due to the attachment of tailings.
As the fields in which heat-sensitive recording materials are used expand, they are exposed to a greater chance of contact with plastics. This results in the recorded image undesirably losing color by reaction with the plasticizer in the plastics. To avoid this problem, the heat-sensitive recording material must have resistance to plasticizers. Furthermore, the recording material must be waterproof so that the recorded image will not lose color even if it is moistened with water. However, none of the known high-sensitivity thermal recording materials provide a recorded image that is resistant to both plasticizers and water.